Encapsulated carbon

Figure 4. The FTIR spectrum of carbon encapsulated in the channels of the MCM-41. The spectrum of the MCM-41 host was subtracted.

Depending on the operation conditions three different types of carbon can be formed whisker-like carbon, encapsulating carbon and pyrolytic carbon. 

The structure of [(Y0H2)3(C03)(A-a-PW9034)2]" [25]. (Reprinted with permission from T.M. Anderson, W.A. Neiwert, and C.L. HiU, Yttrinm polyoxometalates. Synthesis and characterization of a carbonate-encapsulated sandwich-type complex, Inorganic Chemistry, 42, no. 26, 8600-8602 (Figure 1), 2003. 2003 American Chemical Society.)... 

The novel properties of magnetic nanoparticles are in focus of many fundamental research and practical applications [1,2], It is difficult to prevent metallic magnetic (Fe, Co, Ni) nanoparticles from oxidization under conventional experimental conditions. Several techniques, such as carbon encapsulation, reagent stabilizing, and passivation of nanoparticles, have been developed to protect metallic particles. 

Several fluid bed processes are under development for production and encapsulation of nanoparticles, for example, WC-Co composites, bioceramics (i.e., calcium phosphate hydroxyapapite), carbon encapsulation of iron magnetic nanoparticles, and carbon nanotubes. These nano- or ultrafine powders have broad industrial and pharmaceutical applications. Production processes usually include solution preparation (sol-gel), drying, calcination, and sintering. The last three steps may be realized in a fluidized bed, but fluidization of nano- and ultrafine powders is very difficult because of strong interparticle forces. 

Build up of carbon on the surface can necessitate replacement of the catalyst. Crystalline carbon encapsulates nickel and deactivates the catalyst. However, carbon may also dissolve in nickel and reprecipitate at a grain boundary, resulting in a nickel particle being raised on a column of carbon [3,4]. The characteristic whisker carbon produced in this way (Figure 5) blocks the reactor and causes high pressure drop without, necessarily, affecting catalytic activity. This results from the fact that the nickel particle on the tip of the carbon whisker remains accessible to the gas and continues to promote steam reforming. 

Whisker carbon Encapsulating polymers Pyrolytic carbon... 

Carbon formation on steam reforming catalysts takes place in three different forms whisker-like carbon, encapsulated carbon, and pyrolytic carbon as described in Table 2.2 [1]. Whisker-like carbon grows as a fiber from the catalyst surface with a pear-shaped nickel crystal on the end. Strong fibers can even break down catalyst particles increasing the pressure drop across the reformer tubes [4], The carbon for whisker formation is formed by the reaction of hydrocarbons as well as CO over transition metal catalysts [1], The whisker growth is a result of diffusion through the catalyst and nucleation to form a long carbonaceous fiber. 

The Development of Mound Growths. The mound carbon encapsulates the metal and prevents it from taking part in the reaction until particulate growth has caused substantial break-up of the bulk metal. Similar types of deposit have been reported in the Ni/C2H2 reaction at 990°C and Fe/CIfy system at 1100°C(19). A reduction in reactivity caused by encapsulation was reported for the Fe/CjHg deposition reaction(20)... 

Enviro-Stab 1093. [Monson Chem.] Basic white lead carbonate, encapsulated. 

Atomic carbon, encapsulating and filamentous carbon are the most important types of carbon formed. It is generally accepted that filament carbon formation (13) involves the formation of adsorbed surface carbon, dissolution and segregation of surface carbon, diffusion of carbon through Ni particles and precipitation of filaments. The mechanism of carbon formation (12,13) is illustrated in Fig. 1. CNi,f is the concentration of carbon dissolved in nickel at the front of the particle, just below the selvedge, and CNi.r is the concentration of carbon dissolved in nickel at the rear of the particle (support side). The properties of the carbon on the front side and the filamentous carbon on the rear side are rather different. The different... 

Arc discharge technique This is similar to that used for fullerene synthesis, was applied for the preparation of carbon-encapsulated Ni, Co, or Fe nanoparticles. 

McHenry, MJi. and Subramoney, S., Synthesis, structure, and properties of carbon encapsulated metal nanoparticles, mFnllerenes Chemistry, Physics and Technology, Kadish, K.M. and Ruoff, R.S., Eds., Wiley-Interscience, New York, 2000 (Chapter 19), pp. 839-885. 

At a laboratory scale, cmitinuous production yields irrai-based particles of 20-50 run at a production rate of >10 g/h. Carbon-encapsulated iron carbide (C/FesC) combines exceptionally high saturation magnetization (140 emu/ g), air stability (up to 200°C), and resistance against acidic dissolution (1 week in 24% HCl). Top graphene-like carbon layer can be covalently functionalized with various linkers to chemically design the particle surface... 

Core-shell carbons can also be produced by floating catalysts. For example, a picric-acid-detonation-induced pyrolysis of FcH or Fe(CO)5 gave carbon-encapsulated Fe NPs (5-20 nm) [29]. The reaction is characterized by a self-heating and extremely fast process. Tubular structures are formed at a high C/Fe ratio in this reaction. The pyrolysis of metallocenes such as FcH, cobaltocene, or nickelocene is known to yield CNTs and metal-fiUed onion-like structures [21]. The wall thickness (diameter) is controlled by the FcH content. Carbons onions have been synthesized in a CVD reactor at a temperature of 900 °C using Fe3(CO)i2 as the catalyst under an Ar/02 atmosphere [29]. 

Carbon Formation. Steam reforming involves the risk of carbon formation by the decomposition of methane and other hydrocarbons or by the Boudouard reaction (reactions (7) -(10)). Reactions (7) - (8) are catalyzed by nickel (Rostrup-Nielsen, 1984a). The carbon grows as a fibre (whisker) with a nickel crystal at the tip. The methane or carbon monoxide is adsorbed dissociatively on the nickel surface (Alstrup, 1988). Carbon atoms not reacting to gaseous molecules are dissolved in the nickel crystal, and solid carbon nucleates at the non-exposed side of the nickel crystal, preferably from Ae dense (111) surface planes. Reaction (10) results in pyrolytic carbon encapsulating the catalyst. 

Ma Y, Ding B, Ji G et al (2013) Carbon-encapsulated F-doped Lt4Ti50i2 as a high rate anode material for LU batteries. ACS Nano 7(12) 10870-10878... 

A comprehensive, systematic work related to Li-sulfur battery systems is described, beginning with the Li anode challenges, carbon-encapsulated sulfur cathodes, and various kinds of relevant electrolyte solutions (29). 

L.J. Gray, Concrete mixtures including carbon encapsulating admixture, US Patent 8871021, assigned to Staker Parson Companies (West Haven, UT), October 28, 2014. 

High ash content is detrimental to carbon conversion for reasons of carbon encapsulation. 

The application of Sn anodes is still hampered by their inherent poor cycling stability resulting from the large volume change. Several strategies have been proposed to overcome this problem. One of the effective strategy is to prepare intermetallic compounds (M M), which consist of an inactive phase M and an active phase M . Another useful approach is either to disperse the nanometer-sized tin-based materials into a carbon matrix or to prepare the carbon-encapsulated hollow tin nano-particles. The carbon component has good elasticity to effectively accommodate the strain of... 

Nowicka AM, Kowalczyk A, Donten ML, Donten M, Bystrzejewski M, Stojek Z (2014) Carbon-encapsulated iron nanoparticles as ferromagnetic matrix for oxygen reduction in absence and presence of immobilized laccase. Electrochim Acta 126 115-121... 

The coimection between carbon nanotubes and other fullerenes has been defined by the observation that the nanotubes were closed by fullerene-like caps or hemispheres. It is interesting to observe that the smallest reported carbon nanotube diameter is the same as the diameter of C60. This is important in evaluating the minimum dimension of carbon nanostructures. It is necessary to identify all types of nanoparticles and nanostructures of the fullerene family (multiwall and/or single-wall nanotubes, carbon-encapsulated metal nanoparticles, fullerene black and soot, carbon onion, nanowhiskers, etc.). For each nanostructure it is possible to define a set of physical and chemical properties and subsequent applications. It is also interesting to explore the interrelationships between the various nanostructured carbon forms, as well as their relation to the traditional forms of ordered carbon atoms such as diamond and graphite. Carbon is a unique material and can be a good metallic... 

Hao, C., Xiao, F. and Cui, Z. (2008) Preparation and structure of carbon encapsulated copper nanopartides. JourruU of Nanoparticle Research, 10,... 

Sergiienko, R., Shibata, E., Suwa, H., Nakamura, T., Akase, Z., Murakami, Y. and Shindo, D. (2006) Synthesis of amorphous carbon nanoparticles and carbon encapsulated metal nanoparticles in liquid benzene by an electric plasma discharge in ultrasonic... 

Cheng MY, Hwang BJ (2010) Mesoporous carbon-encapsulated NiO nanocomposite negative electrode materials for high-rate Li-ion battery. J Power Sourc 195 4977-4983... 

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